Ambulatory medical devices include implantable medical devices (IMDs), wearable medical devices, handheld medical devices, and other medical devices. Some examples of IMDs include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include a combination of such capabilities. The devices can be used to treat patients or subjects using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. Some implantable medical devices can be diagnostic-only devices, such as implantable loop recorders (ILRs) and subcutaneously implantable heart failure monitors (SubQ HFMs). The devices may include electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, or can include one or more sensors to monitor one or more other internal patient parameters. Subcutaneously implantable devices may include electrodes that are able to sense cardiac signals without being in direct contact with the patient's heart. Other examples of IMDs include implantable drug delivery systems or implantable devices with neural stimulation capability (e.g., vagus nerve stimulator, baroreflex stimulator, carotid sinus stimulator, spinal cord stimulator, deep brain stimulator, etc.).
Some examples of wearable medical devices include wearable cardioverter defibrillators (WCDs) and wearable diagnostic devices (e.g., an ambulatory monitoring vest, holter monitor, cardiac event monitor, or mobile cardiac telemetry devices). WCDs can be monitoring devices that include surface electrodes. The surface electrodes may be arranged to provide one or both of monitoring to provide surface electrocardiograms (ECGs) and delivery of cardioverter and defibrillator shock therapy. In some examples, a wearable medical device can also include a monitoring patch worn by the patient such as an adherable patch or can be included with an article of clothing worn by the patient.
Some examples of handheld medical devices include personal data assistants (PDAs) and smartphones. The handheld devices can be diagnostic devices that record an electrocardiograph (ECG) or other physiological parameter while the device is resting in the patient's hand or being held to the patient's chest.
Some medical devices include one or more sensors to monitor different physiologic aspects of the patient. The devices may derive measurements of hemodynamic parameters related to chamber filling and contractions from electrical signals provided by such sensors. Sometimes patients who are prescribed these devices have experienced repeated heart failure (HF) decompensation or other events associated with worsening HF. Symptoms associated with worsening HF include pulmonary and/or peripheral edema, dilated cardiomyopathy, or ventricular dilation. Early attention to signs and symptoms of HF decompensation is needed for the health of the patient and allows early initiation of treatment.